Rod tags are well known RFID devices which usually comprise a ferrite rod around which a wire is wound to form an antenna and the antenna is connected then to a chip, thus forming the tag. Typically, such tags are encapsulated in a glass or synthetic casing to form the finished product.
The technology of fabricating such rod tags is well known in the art. Prior art documents disclose in particular the step to bond the extremity of the winded wire (antenna) directly on the pads of a RFID chip: this is also called direct bonding.
Prior art documents include for example the following publications, all incorporated by reference in the present application.
U.S. Pat. No. 5,393,001 discloses a coil winding equipment for winding an antenna on a core, for example a ferrite core that is used in a rod tag.
U.S. Pat. No. 5,572,410 discloses an integrated circuit device having a winding connected to an integrated circuit solely by a wire. More specifically, this patent discloses a rod tag with a core, such as a ferrite core, on which a winding is produced forming an antenna, two ends of the antenna being soldered to contacts of an electronic circuit. In this classical configuration, the electronic circuit is placed at the end of the rod which is cylindrically shaped.
U.S. Pat. No. 7,825,869 discloses miniature transponders in the shape of rod tags. The disclosed tags comprise a capsule enclosure housing which contains a magnetic antenna core, such as a ferrite core, with a shaped form to provide space for an integrated circuit also included in the capsule enclosure housing. More specifically, in this prior art, embodiments are described that effectively utilize substantially all the available space within a given enclosure or capsule to accommodate the largest possible antenna assembly including a ferrite core and antenna coil/coils windings while still allowing a reliable functional attachment of an integrated circuit to the wire leads of the antenna ferrite core within the same enclosure. The wired leads may be direct bonded to the integrated circuit. As described in this prior art reference, an antenna ferrite core (or magnetic core), which extends substantially through the full length of the available space within a capsule enclosure, is shaped in such a way as to allow the miniature, direct-bonded integrated circuit to be located within the space provided by the pre-shaped end of the ferrite core. This use of the pre-shaped space allows for placement of the IC without increasing the overall length of the assembly beyond the length of the ferrite core and without requiring an increase in the size of the capsule. After placement of the direct-bonded integrated circuit (IC), the IC can be left loose within the capsule enclosure, or it can be glued to the side of the ferrite core after the direct-bonding process has been accomplished, as desired. Protection against shock and damage by vibration within the encapsulation can be accomplished by insertion of stabilizing epoxy or other material within the capsule. This stabilizing epoxy surrounds the ferrite core and the IC to hold them in place. In one embodiment of U.S. Pat. No. 7,825,869 the integrated circuit is not positioned in a preshaped space of the core but is positioned adjacent a side of the core over the windings. For this embodiment, assuming the core remains relatively the same size, the capsule containing the tag would have to be larger than the capsule used for the other depicted embodiments where the IC is placed in a in space of the core in order to make room for the integrated circuit. Still, the main teaching of this prior art is to provide a predetermined space in the rod to place the IC in said space.
A drawback of the classical rod tag configurations as disclosed in the above prior art is that the chip is positioned at the extremity of the rod, adding its own length to the total tag length. In order to obtain the maximal tag reading range, it is desired to maximalize the length of the magnetic core on which the antenna wire is winded. Ideally, it should match the available length in its encapsulation (i.e. glass tube).
A solution is given in U.S. Pat. No. 7,825,869 but here the rod has to be modified which has a consequence on its symmetry and renders its handling more difficult. In particular, its position and that of its space have to be known to ensure a proper assembly of the disclosed device.
Another solution is given in US 2011/0259965. In this publication, the antenna core, for example a ferrite core, comprises an elongated structure with a central section and end sections. The central section is used to install the antenna coil and the end sections have top and bottom planar surfaces for mounting an integrated circuit. Accordingly, the core is not symmetrical either (as in U.S. Pat. No. 7,825,869) and its position has to be precisely defined during the manufacturing process in order to be able to mount the circuit at the right place. The method disclosed includes the steps of attaching the antenna to the core, attaching the circuit to whichever of said surfaces that is proximate to the leads of the installed antenna and connecting the leads to the circuit.
As mentioned previously, this known device has the disadvantage of a non-symmetrical ferrite core which implies in addition that a manufacturing step is necessary to shape the core and has the consequence of a loss of material. This device and the necessary production process is therefore time consuming and more expensive.